Deadman seat actuated brake

ABSTRACT

A spring for urging the application brakes of a fork-lift truck is overpowered by a toggle joint moved toward its dead center by depression of the knee thereof by the weight of the operator in the operator&#39;&#39;s seat. The mechanical advantage provided by the toggle joint between the seat and the brake-applying spring is such that the seat may bounce normally without permitting application of the brake. Further, the seat can be tilted forwardly for access to the truck without additional attention to disconnection and reconnection of parts.

United States Patent Cottrell [451 May23, 1972 DEADMAN SEAT ACTUATEDBRAKE Samuel H. Cottrell, Mound, Minn.

Assignee: White Farm Equipment Company Filed: June 5, 1970 Appl. No.:43,854

Inventor:

U.S. Cl ..l80/l0l, 74/520, 188/109 Int. Cl ..B60b 7/12 Field ofSearch..180/10l, 102; 74/520,521;

References Cited UNITED STATES PATENTS 7/1966 Ryskamp 180/101 6/1925Deckert ...74/520 X 10/ l 965 McCann et a1. ..74/52O FOREIGN PATENTS ORAPPLICATIONS 813,092 5/ 1959 Great Britain ..74/520 OTHER PUBLICATIONSProduct Engineering 1953 Annual Handbood, Toggle Linkage Applications inDifferent Mechanisms," pp. 26 & 27.

Primary Examiner-Benjamin Hersh Assistant Examiner-John P. SilverstrimAttorney-Watts, I-Ioifmann, Fisher & Heinke [57] ABSTRACT A spring forurging the application brakes of a fork-lift truck is overpowered by atoggle joint moved toward its dead center by depression of the kneethereof by the weight of the operator in the operators seat. Themechanical advantage provided by the toggle joint between the seat andthe brake-applying spring is such that the seat may bounce normallywithout permitting application of the brake. Further, the seat can betilted forwardly for access to the truck without additional attention todisconnection and reconnection of parts.

19 Claims, 4 Drawing Figures PATENTEUmzs I972 sum 1 [IF 2 INVENTOR.SQMUEL H. COTTBELL BY w 1 ML ATTOEA/EY PATENTEDMAY 23 I972 3 664,454

sum 2 [IF 2 INVENIUR. SAMUEL COTT/PELL ATTORNEYS lax ZZZ? W DEADMAN SEATACTUATED BRAKE CROSS REFERENCE TO RELATED APPLICATION BACKGROUND OF THEINVENTION 1. Field of the Invention Thepresent invention is directed tovehicle brake-actuating mechanisms and more particularly to a so-calleddeadman brake actuating mechanism for vehicles having an operators seat,and which mechanisms automatically apply the brakes whenevertheoperators seat is unoccupied.

2. Prior Art.

ln the past, vehicles such as fork-lift trucks and golf carts have-beenequipped with devices known as deadman brakes. In such vehicles, thetypical deadman brake is actuated by the operators seat. Usually, theseat is spring biased upwardly so that whengthe operator leaves thetruck, the seat elevates. Elevation of the seat actuates a mechanismwhich causes brakes to be applied.

Prior deadman brake proposals have included mechanical linkages whichapply the brakes when the seat is elevated and release them when theseat is depressed. Among other deficiencies, these linkages have beensusceptible to intennittent, unintended brake applications when thevehicle is traversing roughterrain. For example, if a fork-lift truckequipped with one of the prior art deadman linkages passed over a bumpat a relatively great rate of speed, the bouncing of the driver couldcause unintended and undesired brake application. Prior mechanicallinkages have failed to accommodate the bouncing in that they aretypically designed such that the maximum rate of brake applicationoccurs as the seat commences to rise. Since the maximum rate of brakeapplicationoccurs as the seat commences to rise, the amount of bouncingwhich can be accommodated without unintended brake application. isminimized.

The prior deadman brakes have often had other disadvantages. In someinstances, the mechanical connections between the seat andbrake-actuating mechanisms were unduly complicated. In addition tothecomplexity in assembly and the cost resulting from unduly complexmechanisms, they also had thedisadvantage of impeding removal of theseat and access to the truck mechanism beneath the seat.

THE PRESENT INVENTION brakes are held in a released condition by atoggle joint held' approximate to a straight line or dead centerposition by the weight of the vehicle operator. The weight of theoperator is applied to the knee of the toggle joint by a connection withthe seat.

The mechanical advantage of the movement of the seat in overcoming theforce of the brake-actuating spring is such that the seat may bouncethrough a relatively considerablev range without corresponding movementof the brake-applying mechanism. This relatively large range of bouncingis achieved through the provision of the toggle joint which issubstantially at straight line or dead-center position when the brakesare released. Because of this, the rate of brake application isinitially at a low rate and increases as the seat is raised and thetoggle joint flexes such that its effective length is shortened.

Accordingly, a major object of the invention is the provision of a newand improved seat-controlled vehicle-brake-actuating mechanism ofthedeadman type mentioned.

Another object of the invention is the provision of a deadman-brakeconstruction which can be assembled as a unit and readily andinexpensively installed in a truck.

Other objects and-advantages of thezinvention will be apparent from thefollowing description of a preferred form thereof, reference being madeto the accompanying drawings in which:

FIG. 1 is a fragmentary'side view of a fork-lift truck embodying theinvention;

FIG. 2 is a fragmentary side elevational viewof linkage for controllingthe brakes of the lift truck;

FIG. 3 is a plan view of the linkage shown in FIG. 2; and

FIG. 4 is an-end view of the linkage shown in FIG. 2.

BRIEFDESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings,a fork-lift truck is shown at 10. The truck 10: includes a operator'sseat 11 and a brake mechanismwhich is actuated by movement of suitablelinkage, a portion of which is shown at 12. The brake mechanism is ofconventional construction and the details thereof are unnecessary to anunderstanding of the present invention. Suffice it to say the brakemechanism applies the brakes when the link 12 is moved to the left, asviewed in FIGS. 1 and 2, and the brakes are released when the link movesto the right.

The truck 10 includes a hood 13 which encloses part of the truckmechanism and forms a support for the seat 11. The hood is hingedto thetruck body at-l4 so thatit may be swung forwardly for access to theinterior of the truck. The forward portion of the seat 11 is pivoted tothe hood at 15 and may be moved about its pivot relative to the hood, asviewed in FIG. 1.

A brake-actuating assembly is shown generally at 16. When the seat 1 lis unoccupied, the brake linkage 12 is shifted to the left, as shown infull lines in FIG. 1, to apply the brakes of the truck by thebrake-actuating assembly 16. When the seat is occupied, thebrake-actuating assembly is overpowered and the linkage l2is shifted tothe right to release the brakes.

The actuatingassembly 16 has a base 17. The base 17 is preferably formedofa metal bar bent adjacent one end thereof to provide an uprightportion 20. A brace bar 21 is welded betweenthe base proper and theupright portion 20 to provide rigidity to the base. The base 17 isattached to the frame of the truck below the seat 11 by suitable means,not shown.

An actuator arm 22 is pivotally connected to the forward end of the base17 by a pin 23. The pin 23 is supported in openings through a pair ofspaced lugs 24 welded to the base. The linkage 12 is connected to theupper end of the arm 22, a pin 23a, a lug 25, and a clevis and pin 26.

The arm 22 is urged counterclockwise about its pivot by abrake-actuating tension spring 27. One end of the spring 27 is attachedto an eye 30 connected to the arm 22. The opposite end of the spring 27is secured to an eye bolt 31 attached to the upright portion 20.

counterclockwise movement of the arm 22 is limited by a stop screw 32.The stop screw 32'is a cap screw which is threaded through anopening ina bracket 33. The bracket 33 is welded to the base 17. The stop screw 32is secured in an adjusted positionby a lock nut 34. Thespring 27 is ofsufiicient strength to move the linkage l2 and firmly apply the brakeswhen the arm 22is moved to the screw'32.

The arm 22 is adapted to be shifted clockwise, as seen in FIGS. 1 and 2,about its pivot from the solid line to the phantom line position ofFIG. 1. When the arm 22 is shifted to its phantom position, the linkage12 is in its brake-release position. This release movement of the arm 22is accomplished by a toggle joint comprised of two toggle arms 35, 36.The toggle arms 35, 36 are pivotally connected to one another atadjacent ends by a pivot pin 40. The connected ends of the arms 35, 36for a knee 38 of the toggle joint. The arm 35 is pivotally attached tothe arm 22 by the pivot pin 23a. The arm 36 is attached to an anchorbracket 42 by a pivot pin 41.

The arm 35 is formed of two bars 43, 44 which are spaced apart by thepins 23a, 40, while the arm 36 is a single bar extending between thebars 43, 44. The bracket 42 comprises 4 two spaced lugs welded to theupright 20 of the base. The bar 36 extends between these lugs of thebracket 42.

When the spring 27 moves the actuating arm 22 to the stop 32, or nearlyso, the arms 35, 36 will be moved to a brake apply position. When in thebrake apply position the arms 35, 36 are at an angle considerably lessthan 180 as seen in FIG. 2. In this position the knee 38 of the togglejoint is raised considerably above the straight line or dead-centerposition of the toggle joint which is represented by the broken line 45in FIG. 2 and shown in phantom in FIG. 1.

The operators seat 1 1 is provided with an abutment 45. The abutment 45is in the form of a flange or bar projecting from the bottom of theseat. The bottom edge 46 of the abutment 45 rests on the arm 36 at theknee 38 when the seat 11 is in its brake apply position shown in fulllines in FIG. 1 and in its occupied brake-release position which isshown in phantom. When the operator leaves the seat 11, the force of thespring 27 causes the toggle joint to buckle. This raises the toggle knee38 and the seat upwardly at the same time the link 12 is moved to applythe brakes. When the seat is occupied the weight of the operatordepresses the seat and forces the knee 38 of the toggle joint downwardlyto the brake-release position.

During movement of the truck over rough surfaces the seat 11 tends tobounce and momentarily raise about its pivot 15 from time to time.Because the knee of the toggle joint can raise an appreciable distancefrom the position shown in broken lines in FIG. 1 without imparting acorresponding distance of movement to the lever 22, the bouncingmovements of the seat 1 l are normally insufficient to permitapplication of the brakes by the force of the spring 27. Furthermore,when the knee of the toggle joint is in its depressed position with thetoggle arms 35, 36 nearly straight, the vertical component of force ofthe spring 27 acting at the knee is relatively light. Thus, the tendencyof the force of spring 27 to accentuate bouncing movements of the seat 1l is minimal.

It will be appreciated that the brake-applying mechanism 16 can beconveniently assembled to the base 17 which may then be installed on thetruck by routine procedures. Among other advantages, this permits thedeadman seat device to be offered as an accessory. It can be readilyinstalled in the field on trucks which have not been equipped withdeadman brake arrangements. The fact that the operating connectionbetween the seat 1 l and the actuating mechanism 16 is effected by theabutment 45 merely resting on the toggle joint knee facilitates theinstallation of the mechanism on the truck and also permits the hood 13with the seat thereon to be temporarily removed to its open position andreplaced without specifically uncoupling and recoupling the seat withthe brake actuating mechanism.

Although the invention has been described in its preferred form with acertain degree of particularity, it is understood that the presentdisclosure of the preferred form has been made only by way of exampleand that numerous changes in the details of construction and thecombination and arrangement of parts may be resorted to withoutdeparting from the spirit and the scope of the invention as hereinafterclaimed.

What is claimed is:

1. In a fork-lift truck having a brake system and a seat movably mountedon the truck for movement from an occupied position to an unoccupiedposition, an improved deadman seat arrangement comprising:

a. a brake application mechanism mounted on the truck and connected tothe brakes so as to control their application;

b. structure including linkage means interposed between the seat andsaid brake application mechanism for actuating said brake applicationmechanism so as to apply the brakes when the seat is moved from itsoccupied position to its unoccupied mechanism;

c. biasing means connected to said linkage means and normally biasingsaid linkage means toward a brake applied position;

d. said linkage means being arranged to shift said brake applicationmechanism from its brake applied position to a brake release positionagainst the action of the biasing means upon movement of the seat fromits unoccupied to its occupied position; and,

e. said linkage means being constructed such that the rate of movementof said brake application mechanism increases throughout its brakeapplication movement as said linkage means is shifted from its brakerelease to its brake applied position whereby the amount of seatmovement that can be accommodated by the deadman brake arrangement asthe truck traverses rough terrain or the like is maximized.

2. The fork-lift truck of claim 1, wherein said linkage means comprisesa pair of arms pivotally connected together near adjacent end portionsand movable from a position of one relative angle when in the brakerelease position to a more acute relative angle when in thebrake-applied position, said connected end portions being coupled to theseat and other end portions of one of the arms being coupled to saidbrake application mechanism.

3. The fork-lift truck of claim 2, wherein said arms are substantiallyin alignment when in the brake-release position.

4. In a vehicle having a frame structure, an operator's seat movablerelative to the frame structure between occupied and unoccupiedpositions, and a brake system, and improved deadman brake control systemfor applying the brakes at an increasing rate as the seat moves from theoccupied position to the unoccupied position, comprising: 7

a. a toggle joint formed by two arms pivotally connected at adjacentends and having opposite ends movable away from each other duringmovement of said arms toward the deadcenter position of said togglejoint, and movable toward each other during buckling movement of saidtoggle joint;

b. seat connection means interconnecting the seat and the connected endsof said arms such that buckling of said toggle joint elevates the seat,and depression of the seat moves said arms toward the deadcenterposition of said toggle joint;

c. actuating means interconnecting the brake system and said togglejoint so as to actuate the brakes in response to movement of saidopposite ends toward each other, and to release the brakes in responseto movement of said opposite ends away from each other;

d. biasing means biasing said opposite ends toward each other so as toeffect actuation of the brakes and so as to buckle said toggle joint tothereby elevate the seat;

e. whereby said toggle joint serves to regulate the rate of applicationof the biasing force of said biasing means to the brake system inaccordance with the position of the seat so as to apply the brakes at anincreasing rate throughout brake application movement as the scat movesprogressively toward the unoccupied position thereby maximizing theamount of seat movement that can be accommodated without significantbrake application as the vehicle traverses rough terrain which causesthe seat to oscillate toward the unoccupied position.

5. The vehicle of claim 4, wherein:

a. said actuating means connects with one of said opposite ends of saidarms; and

b. an anchor means anchors the other of said opposite ends to said framestructure.

6. The vehicle of claim 5, wherein said seat connection means comprisesan abutment means on the seat resting on said toggle joint at theposition of interconnection of said arms.

7. The vehicle of claim 5, wherein the frame structure includes a basestructure supporting said anchored end and sup porting at least aportion of said actuating means, said biasing means comprising springmeans connected at one end to said base structure and at the other endwith said actuating means.

8. The vehicle of claim 4, additionally including stop means to limitthe movement of said actuating means by said biasing means.

9. In a vehicle having a frame structure, an operators seat movablerelative to the frame structure between occupied and unoccupiedpositions, and a brake system, an improved deadman brake control systemfor applying the brakes at an 'increasing rate as the seat moves fromthe occupied position to the unoccupied position, comprising:

a. a toggle joint formed by two arms pivotally connected at adjacentends;

b. means connecting said toggle joint to the frame structure to theoperators seat, and to the brake system such that the brakes arereleased during movement of said arms toward the deadcenter position ofsaid toggle joint, and such that the brakes are applied during bucklingmovement of said toggle joint, said means comprising:

i. seat connection means interconnecting the seat and the 1 connectedends of said arms such that buckling of said toggle joint moves the seattoward the unoccupied position, and movement of the seat toward theoccupied position moves said arms toward the deadcenter position of saidtoggle joint;

ii. anchor means anchoring the other end of one of said.

arms to the frame structure;

iii. actuating means movably supporting the other end of the other ofsaid arms for movement relative to the frame structure and connectingwith the vehicle brake system so as to apply the brakes when saidactuating.

means moves toward the anchored end of said toggle joint during bucklingof said toggle joint and to release the brakes when said actuating meansmoves away 1 from said anchored end;

c. spring means biasing said arms away from the deadcenter position ofsaid toggle joint so as to move the seat to the unoccupied position andeffect application of the brakes; and;

d. the rate of application of the brakes being controlled by theaforedescribed arrangement of said toggle joint suchthat initialmovement of the seat toward the unoccupied position will result in aslower brake application rate than will each successive increment ofseat movement throughout brake application movement, whereby said togglejoint regulates the application of the biasing force of said springmeans to the brake system so as to apply-the brakes with increasingforce as the seat moves progressively toward the unoccupied position.

10. The vehicle of claim 9, wherein said seat connection means comprisesan abutment means'on the seat resting on said toggle joint at theposition of interconnection of said arms.

11. The vehicle of claim 9, wherein additionally including .the stopmeans to limit the movement of said actuating means .by said biasingmeans.

12. In a fork-lift truck having a supporting frame, an operators seatmovably carried on the frame for movement between an occupied positionand an unoccupied position,

. and a brake system, an improved deadman brake control. system forapplying the brakes at an increasing rate as. the seat moves from theoccupied position to the unoccupied position, comprising:

.a. linkage means having input and output portions, said input portionbeing movable between first and. second.

position, said output portion being movable-respectively between thirdand fourth positions in response to movement of said input portionbetween said first and second positions;

b. said linkage means being arranged such that each succes- -tivelysmallcorresponding output portion movemennbut the final movement of'saidinput portion will result in a relatively large corresponding outputportion movement;

c. seat connection means interconnecting the seat and said inputportionsuch that said input portion is in said first position when theseat is inthe occupied position, and said input portion is in saidsecond position when the seat is inthe unoccupied position;

d. actuating means interconnecting the brake system and said outputportion such thatthe brakes are released when said output portion is insaid third position, and brake application is effectedwhen said outputportion is in said fourth position; and,

e. biasing means biasing said input portion to said. second position andsaid output portion to said fourth position;

f. whereby said linkage serves to regulate the rate of application ofthe biasing force of said biasing means to the brake system inaccordance with the position of the seat I so as to apply the brakes atan increasing rate as the seat moves progressively toward the unoccupiedposition thereby maximizing the amount of seat movement that canbeaccornrnodated without significant brake application as the vehicletraverses rough terrain which causes the seat to oscillate toward theunoccupied position.

13. The fork lift truck of claim '12, wherein said linkage meanscomprises a pair of arms pivotally connected together at, adjacent ends,said connected ends comprising said input portion, the other end of theone of said arms comprising said output portion, said arms being movablebetween a brake release position .of one relative angle, and a brakeapplication position of a more acute angle.

14. The fork lift truck of claim 13, wherein said arms are substantiallyin alignment when in said brake release position.

15. In a vehicle having a frame structure, an operators seat movablerelative to the frame structure between occupied and unoccupiedpositions, and a brake system, an improved deadman brake control systemfor applying the brakes as the seat moves from the occupied position tothe unoccupied position, comprising:

a. a toggle joint having two arms pivotally connected near adjacent endsand having opposite ends movable away from ,each other during movementofsaid arms toward a deadcenter position of said toggle joint, and movabletoward each other during buckling movement of said tog- 'gle joint;

b. connection means pivotally connecting said arms to said frame nearsaid opposite ends while permitting relative buckling movement of thearms;

c. seat connection means interconnecting the seat and the arm connectionsuch that buckling of said toggle joint elevates the seat, anddepression of .the seat moves said arms toward the dead center positionof said toggle joint;

d. actuating means interconnecting the brake system and said togglejoint so as to actuate the brakes in response to movement of saidopposite ends toward each other, and to release the brakes in responseto-movement of said opposite ends away from each other;

e. a spring biasing means connected to andxbiasing said opposite endstoward each otherso as to effect actuation of the brakes and so as tobuckle said toggle joint to thereby elevate the seat;

f. whereby as said toggle joint approaches its dead center position, theforce exerted by said biasing means through said toggle joint upon theseat decreases so as to minimize the upward force exerted on the seatwhen the seat is in the occupied position.

16. The vehicle of claim 15, wherein said toggle joint serves toregulate the rateof application of the biasing force of said biasingmeans to the brake system inaccordance with the position of-the seat soas to apply the brakes at an increasing rate throughout brakeapplication movement as the seat moves progressively upwardly toward theunoccupied position, whereby the amount of seat movement that can beaccommodated without significant brake application is maximized, whilethe effective force on the occupied seat tending to cause the operatorto bounce as the vehicle traverses rough terrain is minimized.

17. The fork lift truck of claim 15, wherein said arms are substantiallyin alignment when in said brake release position.

18 The device of claim 15, wherein said connection means comprises apivot connecting one of the arms to the frame and a link pivotallyconnected to the frame and to the other of the arms.

19. In a vehicle having a frame structure, an operator's seat movablerelative to the frame structure between occupied and unoccupiedpositions, and a brake system, an improved deadman brake control systemfor applying the brakes as the seat moves from the occupied position tothe unoccupied position, comprising:

a. a toggle joint having two arms pivotally connected near adjacent endsand having opposite ends movable away from each other during movement ofsaid arms toward a dead center position of said toggle joint, andmovable toward each other during buckling movement of said toggle joint;

b. seat connection means interconnecting the seat and the arm connectionsuch that buckling of said toggle joint elevates the seat, anddepression of the seat moves said arms toward the dead center positionof said toggle joint;

0. actuating means interconnecting the brake system and said togglejoint so as to actuate the brakes in response to movement of saidopposite ends toward each other, and to release the brakes in responseto movement of said opposite ends away from each other;

d. a tension coil spring biasing said opposite ends toward each other soas to efiect actuation of the brakes and so as to buckle said togglejoint to thereby elevate the seat;

e. said coil spring positioned so as to intersect the line of movementof said connection such that should said arms of said toggle joint tendto move past said dead center position, said toggle joint will engagesaid spring at a position intermediate its ends;

f. whereby as said toggle joint approaches its dead center position, theforce exerted by said biasing means through said toggle joint upon theseat decreases so as to minimize the upward force exerted on the seatwhen the seat is in the occupied position.

=0 III

1. In a fork-lift truck having a brake system and a seat movably mountedon the truck for movement from an occupied position to an unoccupiedposition, an improved deadman seat arrangement comprising: a. a brakeapplication mechanism mounted on the truck and connected to the brakesso as to control their application; b. structure including linkage meansinterposed between the seat and said brake application mechanism foractuating said brake application mechanism so as to apply the brakeswhen the seat is moved from its occupied position to its unoccupiedmechanism; c. biasing means connected to said linkage means and normallybiasing said linkage means toward a brake applied position; d. saidlinkage means being arranged to shift said brake application mechanismfrom its brake applied position to a brake release position against theaction of the biasing means upon movement of the seat from itsunoccupied to its occupied position; and, e. said linkage means beingconstructed such that the rate of movement of said brake applicationmechanism increases throughout its brake application movement as saidlinkage means is shifted from its brake release to its brake appliedposition whereby the amount of seat movement that can be accommodated bythe deadman brake arrangement as the truck traverses rough terrain orthe like is maximized.
 2. The fork-lift truck of claim 1, wherein saidlinkage means comprises a pair of arms pivotally connected together nearadjacent end portions and movable from a position of one relative anglewhen in the brake release position to a more acute relative angle whenin the brake-applied position, said connected end portions being coupledto the seat and other end portions of one of the arms being coupled tosaid brake application mechanism.
 3. The fork-lift truck of claim 2,wherein said arms are substantially in alignment when in thebrake-release position.
 4. In a vehicle having a frame structure, anoperator''s seat movable relative to the frame structure betweenoccupied and unoccupied positions, and a brake system, and improveddeadman brake control system for applying the brakes at an increasingrate as the seat moves from the occupied position to the unoccupiedposition, comprising: a. a toggle joint formed by two arms pivotallyconnected at adjacent ends and having opposite ends movable away fromeach other during movement of said arms toward the deadcenter positionof said toggle joint, and movable toward each other during bucklingmovement of said toggle joint; b. seat connection means interconnectingthe seat and the connected ends of said arms such that buckling of saidtoggle joint elevates the seat, and depression of the seat moves saidarms toward the deadcenter position of said toggle joint; c. actuatingmeans interconnecting the brake system and said toggle joint so as toactuate the brakes in response to movement of said opposite ends towardeach other, and to release the brakes in response to movement of saidopposite ends away from each other; d. biasing means biasing saidopposite ends toward each other so as to effect actuation of the brakesand so as to buckle said toggle joint to thereby elevate the seat; e.whereby said toggle joint serves to regulate the rate of application ofthe biasing force of said biasing means to the brake system inaccordance with the position of the seat so as to apply the brakes at anincreasing rate throughout brake application movement as the seat movesprogressively toward the unoccupied position thereby maximizing theamount of seaT movement that can be accommodated without significantbrake application as the vehicle traverses rough terrain which causesthe seat to oscillate toward the unoccupied position.
 5. The vehicle ofclaim 4, wherein: a. said actuating means connects with one of saidopposite ends of said arms; and b. an anchor means anchors the other ofsaid opposite ends to said frame structure.
 6. The vehicle of claim 5,wherein said seat connection means comprises an abutment means on theseat resting on said toggle joint at the position of interconnection ofsaid arms.
 7. The vehicle of claim 5, wherein the frame structureincludes a base structure supporting said anchored end and supporting atleast a portion of said actuating means, said biasing means comprisingspring means connected at one end to said base structure and at theother end with said actuating means.
 8. The vehicle of claim 4,additionally including stop means to limit the movement of saidactuating means by said biasing means.
 9. In a vehicle having a framestructure, an operator''s seat movable relative to the frame structurebetween occupied and unoccupied positions, and a brake system, animproved deadman brake control system for applying the brakes at anincreasing rate as the seat moves from the occupied position to theunoccupied position, comprising: a. a toggle joint formed by two armspivotally connected at adjacent ends; b. means connecting said togglejoint to the frame structure to the operator''s seat, and to the brakesystem such that the brakes are released during movement of said armstoward the deadcenter position of said toggle joint, and such that thebrakes are applied during buckling movement of said toggle joint, saidmeans comprising: i. seat connection means interconnecting the seat andthe connected ends of said arms such that buckling of said toggle jointmoves the seat toward the unoccupied position, and movement of the seattoward the occupied position moves said arms toward the deadcenterposition of said toggle joint; ii. anchor means anchoring the other endof one of said arms to the frame structure; iii. actuating means movablysupporting the other end of the other of said arms for movement relativeto the frame structure and connecting with the vehicle brake system soas to apply the brakes when said actuating means moves toward theanchored end of said toggle joint during buckling of said toggle jointand to release the brakes when said actuating means moves away from saidanchored end; c. spring means biasing said arms away from the deadcenterposition of said toggle joint so as to move the seat to the unoccupiedposition and effect application of the brakes; and; d. the rate ofapplication of the brakes being controlled by the aforedescribedarrangement of said toggle joint such that initial movement of the seattoward the unoccupied position will result in a slower brake applicationrate than will each successive increment of seat movement throughoutbrake application movement, whereby said toggle joint regulates theapplication of the biasing force of said spring means to the brakesystem so as to apply the brakes with increasing force as the seat movesprogressively toward the unoccupied position.
 10. The vehicle of claim9, wherein said seat connection means comprises an abutment means on theseat resting on said toggle joint at the position of interconnection ofsaid arms.
 11. The vehicle of claim 9, wherein additionally includingthe stop means to limit the movement of said actuating means by saidbiasing means.
 12. In a fork-lift truck having a supporting frame, anoperator''s seat movably carried on the frame for movement between anoccupied position and an unoccupied position, and a brake system, animproved deadman brake control system for applying the brakes at anincreasing rate as the seat moves from the occupied position to theunoccupied position, comprising: a. linkage means havinG input andoutput portions, said input portion being movable between first andsecond position, said output portion being movable respectively betweenthird and fourth positions in response to movement of said input portionbetween said first and second positions; b. said linkage means beingarranged such that each successive increment of movement of said inputportion during movement from said first position to said second positionwill cause an increasingly greater corresponding increment of movementof said output portion, whereby the initial movement of said inputportion will result in a relatively small corresponding output portionmovement, but the final movement of said input portion will result in arelatively large corresponding output portion movement; c. seatconnection means interconnecting the seat and said input portion suchthat said input portion is in said first position when the seat is inthe occupied position, and said input portion is in said second positionwhen the seat is in the unoccupied position; d. actuating meansinterconnecting the brake system and said output portion such that thebrakes are released when said output portion is in said third position,and brake application is effected when said output portion is in saidfourth position; and, e. biasing means biasing said input portion tosaid second position and said output portion to said fourth position; f.whereby said linkage serves to regulate the rate of application of thebiasing force of said biasing means to the brake system in accordancewith the position of the seat so as to apply the brakes at an increasingrate as the seat moves progressively toward the unoccupied positionthereby maximizing the amount of seat movement that can be accommodatedwithout significant brake application as the vehicle traverses roughterrain which causes the seat to oscillate toward the unoccupiedposition.
 13. The fork lift truck of claim 12, wherein said linkagemeans comprises a pair of arms pivotally connected together at adjacentends, said connected ends comprising said input portion, the other endof the one of said arms comprising said output portion, said arms beingmovable between a brake release position of one relative angle, and abrake application position of a more acute angle.
 14. The fork lifttruck of claim 13, wherein said arms are substantially in alignment whenin said brake release position.
 15. In a vehicle having a framestructure, an operator''s seat movable relative to the frame structurebetween occupied and unoccupied positions, and a brake system, animproved deadman brake control system for applying the brakes as theseat moves from the occupied position to the unoccupied position,comprising: a. a toggle joint having two arms pivotally connected nearadjacent ends and having opposite ends movable away from each otherduring movement of said arms toward a dead center position of saidtoggle joint, and movable toward each other during buckling movement ofsaid toggle joint; b. connection means pivotally connecting said arms tosaid frame near said opposite ends while permitting relative bucklingmovement of the arms; c. seat connection means interconnecting the seatand the arm connection such that buckling of said toggle joint elevatesthe seat, and depression of the seat moves said arms toward the deadcenter position of said toggle joint; d. actuating means interconnectingthe brake system and said toggle joint so as to actuate the brakes inresponse to movement of said opposite ends toward each other, and torelease the brakes in response to movement of said opposite ends awayfrom each other; e. a spring biasing means connected to and biasing saidopposite ends toward each other so as to effect actuation of the brakesand so as to buckle said toggle joint to thereby elevate the seat; f.whereby as said toggle joint approaches its dead center position, theforce exerted by said biasing means through said tOggle joint upon theseat decreases so as to minimize the upward force exerted on the seatwhen the seat is in the occupied position.
 16. The vehicle of claim 15,wherein said toggle joint serves to regulate the rate of application ofthe biasing force of said biasing means to the brake system inaccordance with the position of the seat so as to apply the brakes at anincreasing rate throughout brake application movement as the seat movesprogressively upwardly toward the unoccupied position, whereby theamount of seat movement that can be accommodated without significantbrake application is maximized, while the effective force on theoccupied seat tending to cause the operator to bounce as the vehicletraverses rough terrain is minimized.
 17. The fork lift truck of claim15, wherein said arms are substantially in alignment when in said brakerelease position. 18 The device of claim 15, wherein said connectionmeans comprises a pivot connecting one of the arms to the frame and alink pivotally connected to the frame and to the other of the arms. 19.In a vehicle having a frame structure, an operator''s seat movablerelative to the frame structure between occupied and unoccupiedpositions, and a brake system, an improved deadman brake control systemfor applying the brakes as the seat moves from the occupied position tothe unoccupied position, comprising: a. a toggle joint having two armspivotally connected near adjacent ends and having opposite ends movableaway from each other during movement of said arms toward a dead centerposition of said toggle joint, and movable toward each other duringbuckling movement of said toggle joint; b. seat connection meansinterconnecting the seat and the arm connection such that buckling ofsaid toggle joint elevates the seat, and depression of the seat movessaid arms toward the dead center position of said toggle joint; c.actuating means interconnecting the brake system and said toggle jointso as to actuate the brakes in response to movement of said oppositeends toward each other, and to release the brakes in response tomovement of said opposite ends away from each other; d. a tension coilspring biasing said opposite ends toward each other so as to effectactuation of the brakes and so as to buckle said toggle joint to therebyelevate the seat; e. said coil spring positioned so as to intersect theline of movement of said connection such that should said arms of saidtoggle joint tend to move past said dead center position, said togglejoint will engage said spring at a position intermediate its ends; f.whereby as said toggle joint approaches its dead center position, theforce exerted by said biasing means through said toggle joint upon theseat decreases so as to minimize the upward force exerted on the seatwhen the seat is in the occupied position.